This application relates to a turbine blade, wherein the meter sections of film cooling holes extend at an angle and in a direction toward a blade root from the blade tip. In addition, a diffused section of a film cooling hole extends toward the blade tip from a meter section to receive air driven by centrifugal force.
Gas turbine engines are known, and include a plurality of sections which are typically mounted in series. Typically a fan delivers air to a compressor. Air is compressed in the compressor and delivered downstream to be mixed with fuel and combusted in a combustor section. Products of combustion move downstream over turbine rotors. The turbine rotors include a plurality of removable blades which rotate with the rotors, and are driven by the products of combustion. The turbine rotors drive components within the gas turbine engine, including the fan and compressor.
The turbine blades become quite hot from the products of combustion. Thus, it is known to pass cooling air through internal cooling passages within the turbine blades. In one known cooling technique, air is passed outwardly through holes on an outer face of an airfoil of the turbine blade, such that the cool air passes along the outer face. These film cooling holes are designed to maximize the coverage surface area on the blade, which receives the air and also to maximize the time cooling air is kept on a face of the blade.
In the prior art, the film cooling holes have a meter section that typically extend at an angle to the outer face. The angle includes a major component in a direction extending from a blade root and toward a blade tip. In addition, a diffused section extends back from this meter section towards the blade root. This type of film cooling holes is known as shaped or flared holes. The purpose of the diffused section is to slow the speed of the cooling air down as it reaches the face of the blade, such that the air would be less likely to move away from the face, and more likely to move along the face.
However, in the prior art, a centrifugal force applied as the blade rotates, moves the cooling air radially outwardly and toward the blade tip. Thus, the diffused section tends not to be filled with air. This centrifugal force and flow momentum drives the air into the radially outer portions of the holes spaced toward the tip, and leaves the diffused section less filled. Thus, the air exits the film cooling hole at a greater velocity, and does not stay on the face of the blade as long as would be desired.